Weakness and excess fatigue are cardinal signs of musculoskeletal, neurological, and systemic disease. Assessment of strength and fatigue are an essential part of clinical evaluation and therapeutic trials, but currently available methods are unsatisfactory. The goal of this project is to develop a fixed myometry device for measuring strength and fatigue that is suitable for clinical research, clinical assessment, and fitness evaluation. A prototype has been developed with input from patients, clinical investigators, physical therapists, and biostatisticians. This prototype can be adapted for use in various testing situations, and it is portable and easily calibrated. It supports several models for analysis of fatigue. The output data files can be directly exported for biostatistical analysis. Test-retest reliability for measurements of maximal voluntary isometric strength in 20 subjects with multiple sclerosis was excellent. The present application proposes several improvements in the prototype and additional studies to demonstrate reliability and validity of strength and fatigue measurements in healthy subjects and subjects with pathologic weakness and fatigue. PROPOSED COMMERCIAL APPLICATION: The research is expected to produce a protable and flexible system that can measure muscle strength and fatigue. This system should find a market in the areas of therapeutic trials, clinician's offices, physical therapy, and fitness assessment.